The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
FIG. 1 shows a hard disk drive (HDD) 10 that includes a hard disk assembly (HDA) 12 and a HDD printed circuit board (PCB) 14. The HDA 12 includes one or more platters 16, which have magnetic surfaces that are used to store data magnetically. Data is stored in binary form as a magnetic field of either positive or negative polarity. The platters 16 are arranged in a stack. The platters 16 and/or the stack is rotated by one or more spindle motors (one spindle motor 18 is shown). One or more read/write heads (hereinafter, “heads”) read data from and write data on the magnetic surfaces of the platters 16. A single head 20 is shown. Each of the heads includes a write element (e.g., an inductor) that generates a magnetic field and a read element (e.g., a magneto-resistive (MR) element), which senses the magnetic field on one of the platters 16. The heads are mounted at a distal end of one or more actuator arms (a single actuator arm 22 is shown). An actuator, such as a voice coil motor (VCM) 24, moves the actuator arm 22 relative to the platters 16.
The HDA 12 includes a preamplifier device 26. The preamplifier device 26 may include amplifiers for amplifying signals received from the heads. When reading data, generated magnetic fields induce low-level analog signals in the read elements of the head 20. The amplifiers amplify the low-level analog signals and output amplified analog signals to a read/write (R/W) channel (hereinafter, “read-channel”) module 28.
The HDD PCB 14 includes the read-channel module 28, a hard disk controller (HDC) module 30, a processor 32, a spindle/VCM driver module 34, volatile memory 36, nonvolatile memory 38, and an input/output (I/O) interface 40. During write operations, the read-channel module 28 may encode the data to increase reliability by using error-correcting codes (ECC) such as run length limited (RLL) code, Reed-Solomon code, etc. The read-channel module 28 then transmits the encoded data to the preamplifier device 26. During read operations, the read-channel module 28 receives analog signals from the preamplifier device 26. The read-channel module 28 converts the analog signals into digital signals, which are decoded to recover the data previously stored on the platters 16.
The HDC module 30 controls operation of the HDD 10. For example, the HDC module 30 generates commands that control the speeds of the one or more spindle motors and the movement of the one or more actuator arms. The spindle/VCM driver module 34 implements the commands and generates control signals that control the speeds of the one or more spindle motors and the positioning of the one or more actuator arms. Additionally, the HDC module 30 communicates with an external device (not shown), such as a host adapter within a host device, via the I/O interface 40. The HDC module 30 may receive data to be stored from the external device, and may transmit retrieved data to the external device.
The processor 32 processes data, including encoding, decoding, filtering, and/or formatting. Additionally, the processor 32 processes servo or positioning information to position the heads over the platters 16 during read/write operations. Servo, which is stored on the platters 16, ensures that data is written to and read from correct locations on the platters 16. In some implementations, a self-servo write (SSW) module 42 may write servo on the platters 16 using the heads prior to storing data on the HDD 10.
The HDA 12 may include a two-dimensional magnetic recording (TDMR) system 50 and/or other system having a trace suspension assembly (TSA) 52 and multiple read elements. The TSA 52 refers to the one or more actuator arms and transmission lines (e.g., transmission lines 54 are shown) extending between the preamplifier device 26 and the heads. The transmission lines (sometimes referred to as traces) are suspended over the platters 16 via the one or more actuator arms. A TDMR system, such as the TDMR system 50, uses multiple heads positioned adjacent each other to read a single track on a surface of a platter. Signals from the heads are processed to counteract, cancel and/or minimize noise (e.g., inter-track noise and backplane noise coupling) detected during the reading of the track. Inter-track noise can refer to magnetic field characteristics detected and associated with one or more tracks adjacent to the track being read. Backplane noise coupling can refer to noise coupling associated with parallel connected transmission lines, where each of the parallel connected transmission lines is connected to a common ground. Reducing noise improves signal-to-noise ratios for improved recovery of data stored on the tracks.
FIG. 2 shows a magnetic recording system 60 that may be used in the HDA 12 of FIG. 1. The magnetic recording system 60 may be a TDMR system and includes read elements 62, transmission lines 64, and a preamplifier device 66. The preamplifier device 66 includes differential amplifiers 68. Each of the read elements 62 is connected to a respective one of the differential amplifiers 68 via a respective one of the transmission lines 64. The differential amplifiers 68 receive single-ended signals from the transmission lines 64, convert the single-ended signals to differential output signals Out1-OutN, and output the differential output signals Out1-OutN, as shown. Gain of each of the differential amplifiers 68 may be adjusted to increase amplitudes of the differential output signals Out1-OutN and/or to improve corresponding signal-to-noise ratios.
As read cycle frequencies increase, noise picked-up by the read elements 62 can increase, which can negatively affect the signal-to-noise ratios. To minimize and/or cancel the noise, a fully differential magnetic recording system may be used instead of the magnetic recording system 60. A fully differential magnetic recording system provides improved common mode noise rejection by providing differential signals from read elements to differential amplifiers. Common mode noise rejection refers to cancellation of noise common to both inputs of a differential amplifier. FIG. 3 shows an example of a fully differential magnetic recording system 70 that may be used in the HDA 12 of FIG. 1.
The magnetic recording system 70 includes read elements 72, transmission lines 74, and a preamplifier device 76. The preamplifier device 76 includes differential amplifiers 78. Each of the read elements 72 is connected to a respective one of the differential amplifiers 78 via a respective pair of the transmission lines 74. The read elements 72 provide differential signals to inputs of the differential amplifiers 78. Noise signals received at the inputs of each of the differential amplifiers 78 may be compared and cancelled by the corresponding one of the differential amplifiers 78. The differential amplifiers 78 provide differential output signals Out1, Out2. Gain of each of the differential amplifiers 78 may be adjusted to increase amplitudes of the output signals Out1, Out2 and/or to improve corresponding signal-to-noise ratios.